Electrical rheostat assembly



Dec. 11, 1956 E. w. DREWITZ ET AL 2,773,965

ELECTRICAL RHEOSTAT ASSEMBLY 5 Sheets-Sheet 1 Filed July 20. 1954 m a ar W mM 0 Q: m 5 W 2! 2M0 ,F Z 0/ 5w Dec. 11, 1956 E. w. DREWITZ ETAL2,773,965

ELECTRICAL RHEOSTAT ASSEMBLY Filed July 20, 1954 3 Sheets-Sheet 2 v QINVENTORS w EIOw/A/WZDPEW/ 7-2., N w V/crae STE/A1 %-M a kw.

1956 E. w. DREWITZ ET AL 2,773,965

ELECTRICAL RHEOSTAT ASSEMBLY 3 Sheets-Sheet 3 Filed July 20, 1954INVENTORS 0W/A/ VKDlest v/ 7-z.

were? STE/Al United States Patent ELECTRICAL RHEUSTAT ASSEMBLY Edwin W.Drewitz and Victor Stein, Flushing, N. Y., as-

signers to De .lur-Amsco Corporation, Long Island City, N. Y., acorporation of New York Application July 20, 1954, Serial No. 444,462

2 Claims. (Cl. 201-48) This invention relates to electrical rheostatsand potentiometers and relates more particularly to improvementspertaining to the manufacture of rheostat parts and their mode ofassembly.

The prime object of our invention is to improve the production techniqueof precision rheostats and potentiometers. In accordance with theprinciples involved, the rheostat parts are designed to comprise aplurality of independent, pre-finished sub-assemblies which lendthemselves to be assembled into a diversified series of rheostats andpotentiometers by simple, rapid and semi-skilled production steps.

One of the principal sub-assembly components of the rheostat of theinvention comprises the resistance element. This is designed so that itmay be prepared in advance, apart from the other rheostat orpotentiometer elements, inspected for electrical characteristics, andthus being finished in all respects may be stocked for subsequentinventory selection and use in the assembling of the complete rheostat.The structure of the resistance element sub-assembly is also such thatit is rendered adaptable for a variety of changes in the distribution ofresistance values for any given resistance winding, to meet varyingneeds of service, this being a factor in the making of a diversifiedgroup of rheostats and potentiometers with the means of the same basicresistance element component.

Another sub-assembly component of the rheostat is the rheostat casing orhousing with the resistance terminals insulatably carried thereby,designed so that the resistance element component may be assembledthereto by a simple drop-fitting step. This casing or housing componentmay itself be prepared by assembling together by simple productiontechniques the necessary parts to form the pre-finished housingcomponent, with insulated terminals ready for electrical connection tothe resistance parts of the rheostat. The casing or housing subassemblycomponent is also designed so that it may be adapted for diversifiedproduction use.

To the accomplishment of the foregoing object, and such other objects asmay hereinafter appear, our invention is directed to the electricalrheostat assembly sought to be defined in the appended claims takentogether with the following description and the accompanying drawings inwhich:

Fig. l is a view of a plurality of rheostats or potentiometers embodyingthe structure of the present invention, the rheostats being shownassembled in tandem relation, the left side rheostat being taken incross-section along the line 1 1* of Fig. 2, and the right side rheostatbeing taken in cross-section along the line 1 1 of Fig. 2.

Fig' 2 is a view of the left side rheostat of Fig. 1 when viewed alongthe line 2-2 of Fig. 1.

Fig. 3 is an exploded view of the parts employed for producing theassembly of the prefabricated resistance element and the casing orhousing of the rheostat embodying the principles of the presentinvention.

Fig. 4 is a perspective view of the prefabricated rheostat casing orhousing carrying the resistance terminals.

Fig. 5 is a perspective view of the assembly of the prefabricatedresistance element and the prefabricated casing or housing therefor.

Fig. 6 is a perspective view of a prefabricated resistance element withvarious modifications for which the same is adaptable.

Fig. 7 is a perspective view of an element employed in the making of theprefabricated resistance element.

Fig. 8 is a perspective view similar to Fig. 6 but showing amodification of the prefabricated resistance element; and

Fig. 9 is a perspective view of a contact plate employed in theproduction of the completed rheostat or potentiometer.

Referring now more in detail to the drawings, and having reference firstto the form of the rheostat or po tentiometer depicted in Figs. 1 to 5of the drawings, the essence of the improvements embodied in the presentinvention comprises an assembly A, as depicted in Fig. 5, made up of asub-assembly casing C carrying the resistance terminals, as depicted inFig. 4, and a sub-assembly resistance element R, as shown at the righthand side of Fig. 3 of the drawings, these parts being shown in finallyassembled relation in the completed rheostat or potentiometer in Figs. 1and 2 of the drawings.

The sub-assembly resistance element R comprises one of the principalsub-assembly components of the rheostat, and consists of a prefabricatedunit designed for being electrically tested and stocked for futureselection and use in the assembling of the completed rheostat. This unitcomprises an accurately ground insulator tube 10 functioning as aretainer for the resistance winding 12 united to the interior wall ofthe insulator tube 10. The winding 12 (made in the usual Way by windingresistance wire around a flexible strip) which may be provided with theterminal bands 14 is fitted to the interior wall of the insulator tube10 and is made to conform to the precision tube by cementing, heat andpressure, pressure being applied by an expanding arbor during the cementcuring cycle. The result is the prefabricated unit R comprising theresistance winding mounted within and firmly united to the precisioninsulator tube 10. This unit is prepared, apart from the otherpotentiometer elements, is passed through the tests for determining itselectrical characteristics and is stored or inventoried well in advanceof its subsequent use in the assembly of any given rheostat.

This resistance unit or sub-assembly R, as thus constructed, is alsorendered adaptable and lends itself for the making of a variety ofchanges in the distribution of the resistance values of the resistancewinding, this being a factor, as heretofore indicated, in the making ofdiversified groups of rheostats or potentiometers by means of the samebasic resistance element component. This latter is indicated in themodifications shown .in Figs. 6 and 7 of the drawings. Referring firstto Fig. 6 of the drawings the resistance unit or sub assembly R is thereshown to comprise a precision insulator 10' and a resistance winding 12'united thereto, the insulator tube being provided with openings ofpredetermined area such as 16, 18 and 20 exposing the back of a selectednumber of turns of the winding, the said openings being filled with aconducting material such as 22 for shorting out the selected turns ofthe resistance winding. This may be readily accomplished in the unit Rby having the outer wall of the insulator tube 10' serve as an accuratemask for spraying low resistance materials in contact with theresistance winding to effectively short out any desired number of turns.This distribution of the resistance value for the resistance winding maybe obtained by insulating tubes having cutouts or openings of differentareas, as is depicted by the insulating tube 12 shown in Fig. 7 havingthe openings 23 and 2d.

The sub-assembly rheostat casing or housing C carrying the resistanceterminals, shown as a sub-assembly in Fig. 4 of the drawings, and towhich the resistance unit R is adapted to be mounted by a simpledrop-fitting step .is, itself, prepared by assembling together by simpleproduction techniques the necessary parts separately shown in Fig. 3 ofthe drawings to form the prefabricated casing or housing component.Essentially the housing component comprises a metal, such as aluminum,tube 25, a number of resistance terminals 28, 28 and means generallydesignated as 3% for insulatably mounting the terminals on the metaltube 26. These parts also comprise connecting strips 32, 32 conductivelyattached to the terminals and adapted for solder connection to theresistance parts of the rheostat.

In Fig. 3 are depicted the parts and the mode of assembling the parts toform this casing or housing section C. The metal tube 26 formed at itsends with male and female grooves 34 and 36 for the purpose of couplingmultiple sections (see Fig. l), is provided with a plurality of orifices38 for the reception of the terminals 23, 28, the terminals beinginsulated by means of the washers iii, so also received and fitted intothe orifices 33. The means (39) for insulatably securing the terminalsin position comprises preferably a first sheetor strip insulator 42 alsoorificed at 44, 44 (for registering with the orifices 3d), and a secondsheet or strip-insulator 46 provided with irregular shaped openings,such as the square openings or orifices 48, 48, the insulator strip -42being adapted to be fitted to the interior wall of the casing tube 26and the insulator 46 being adapted to be fitted to the inside wall ofthe first insulator 42. These insulator strips are accuratelydimensioned so that they may be assembled in the casing section C withtheir ends abutting as indicated for the insulator 46 at 59 (Fig. 4).For insulatably mounting the front of the terminals there is alsoprovided an arcuately shaped insulator piece 52 provided with theregisterable orifices 54, 54. The connecting strips 32, 32 are alsoprovided with registerable orifices 56, d. The terminals 28 are formedwith irregularly shaped end such as the squared head or portions 53 forfitting into the squared openings 48 in the insulator 46. For securingthe terminals in position there may be provided the securing nuts 6%,6i}.

These described parts may be assembled to form the sub-assembly casingsection C in a manner depicted by I the sequential arrangement of theparts in Fig. 3 of the drawings. Connecting strips 32 are arrangedbetween the insulators 42 and .6; these insulators are fitted into thehousing tube 2.6 and the terminals are then threaded through theregistering orifices, the terminals being locked against rotation by theinterfitting of the terminal portions 58 in the squared openings 48, andthe parts are locked in assembled position by the nuts 64 66). Thesub-assembly thus produced, as depicted in Fig. 4, is now ready for thedrop assembly reception of the sub-assembly resistance component.

These sub-assemblies C and R may then be assembled by the simple forcedinsertion of the resistance component R into the casing component C toproduce the unit shown in Fig. 5 of the drawings. The connecting strips32, 32 may have their ends turned down as shown in 5 supported on aninsulating ring Selected ones of the connecting strips may then beconnected by wire attachments 64 to selected sections of the resistancewinding, the end connecting strip 32 being in turn connected to acontact ring 66 as indicated for the left hand rheostat in Fig. 1 of thedrawings.

In Fig. 8 of the drawings we show a modification of the resistance unitwhich permits of the elimination of the insulator strip 46. In thismodification the resistance unit R comprises a precision retainer tube10 to which is united the resistance winding 12 the insulator tube beingformed with longitudinal grooves ss, 68. With this unit R the insulatorstrip 46 may be dispensed with, the longitudinal grooves 68, 68 beingdesigned for the reception of the squared portions 53, 5'3 of theterminals, thereby locking the same against rotation, the connectingstrips 32, 32 being also adapted to be received in for extension fromthese grooves.

A complete rheostat or potentiometer is made by interfitting an end wall70 (see Fig. 9) to an end of the casing tube 26, the hub 72 of said endwall receiving a spacing collar 74 for mounting the rheostat shaft 76 towhich is keyed an insulator plug 78 carrying a contact plate 80. Thecontact plate 80 shown in detail in Fig. 9 is provided with the balancedcontact arms 32 and 84 provided with cylindrical elements 86, 83 forengaging the contact ring 66 (connected to the end terminal 28) thecontact plate being also provided with brush contact elements 99 forriding over and engaging the resistance element 12. A plurality of theseassembled units may be coupled together in tandem form by theinterfitting of the male and female grooves 34 and 36. An end unit of atandem assembly (or a separate rheostat or potentiometer) may be made byforming the end wall 92 (see the left hand unit in Fig. l) integral withthe casing tube 26. A group of rheostats arranged in tandem may belocked against endwise movement of the rheostat shaft 76 by means oflocking rings 94, 94.

The improvements in the technique of producing precision rheostats andpotentiometers of the present invention and the many advantages securedthereby will in the main be fully apparent from the above-detaileddescription thereof. It will be further apparent that many changes maybe made therein without departing from the spirit of the inventiondefined in the following claims.

We claim:

1. A sub-assembly resistance element for drop-fitting into a casing toproduce a rheostat assembly and defining a prefabricated resistanceelement designed for being electrically tested and stocked prior tomaking the rheostat assembly, comprising an accurately pie-dimensionedinsulator tube and a resistance wiring unit united to the interior wallof the insulator tube, said insulator tube being provided with anopening of predetermined area to be filled with a conducting materialfor shorting out selected turns of the resistance winding.

2. The sub-assembly resistance elements of claim 1 in which theinsulator tube is provided with openings of pre-determined locations andareas to be filled with a conducting material for shorting out selectedturn sections of the resistance winding, the outer wall of saidinsulator tube serving as an accurate mask for spraying the con ductingmaterial into said openings.

References Cited in the file of this patent UNITED STATES PATENTS1,947,437 Schellenger Feb. 13, 1934 1,948,774 Siegel Feb. 27, 19342,592,392 Canziani et a1 Apr. 8, 1952

